1. Field of the Invention
The present invention relates generally to polyimides, especially imide oligomers. It relates particularly to a series of phenylethynyl-terminated imide oligomers which can be thermally cured to resins that are useful as adhesives, composite matrices, moldings, films and coatings. The invention also relates particularly to a series of amino phenylethynyl compounds used to terminate the imide oligomers.
2. Description of Related Art
Polyimides are condensation polymers that can be prepared by various routes. The most popular route involves the reaction of an aromatic dianhydride with an aromatic diamine. The intermediate polyamide acid is either thermally or chemically cyclodehydrated to form the polyimide which has a repeat unit of the general type ##STR1## where Ar' is a tetravalent aromatic radical, which can be as simple as 1,2,4,5-tetrasubstituted benzene, or it may be a bis-4-(o-diphenylene) having the general structure ##STR2## where X.dbd.nil, O, S, SO.sub.2, C.dbd.O, etc. Ar' may be any other appropriate tetravalent radical. Ar is a divalent aromatic radical which may be 1,3-phenylene, 1,4-phenylene, 4,4'-oxydiphenylene, 4,4'-biphenylene, 4,4'-thiodiphenylene, 4,4'-carbonyldiphenylene, 4,4'-methylenediphenylene or any other appropriate divalent radical.
Synthesis and characterization of polyimides has been extensively reported in the literature. The preparation of aromatic polyimides by reaction of an aromatic dianhydride with an aromatic diamine, followed by thermal cyclization was first reported in 1963 [G. M. Bower and L. W. Frost, J. Polym. Sci. A1, 3134 (1963)] with patents awarded in 1965 (W. M. Edwards, U.S. Pat. Nos. 3,179,614 and 3,179,634 and A. L. Endrey, U.S. Pat. Nos. 3,179,631 and 3,179,633). Several reviews on polyimides have been published [C. E. Sroog, "Polyimides" in Encyclopedia of Polymer Sci. and Technology (H. F. Mark, N. G. Gaylord and N. M. Bikales, ed.) Interscience Pub., New York, 1969, Vol. 11, pp. 247-272; N. A. Adrova, M. I. Bessonov, L. A. Lauis and A. P. Rudakov, Polyimides, Technomic Pub. Co., Inc., Stamford, Conn., 1970].
Wholly aromatic polyimides are known for their exceptional thermal, thermooxidative and chemical resistance, but are generally difficult to process as structural adhesives or composite matrices. Several polyimides such as Kapton.RTM. (DuPont), PI-2080 (Dow Chemical, licensed to Lenzing), XU-218.TM. (Ciba-Geigy), Ultem.RTM. (General Electric) and LaRC.TM.-TPI (Mitsui Toatsu) are commercially available and used as fibers, films, moldings, adhesives or composite matrices.
The incorporation of ethynyl groups in polyimides has been reported in the literature, typically as terminal groups to yield acetylene-terminated imide oligomers (ATI). Thermid-600.TM., an oligoimide with acetylene end groups was first developed at the Hughes Aircraft Co. [N. Bilow, A. L. Landis and L. J. Miller, U.S. Pat. No. 3,845,018 (1974); A. L. Landis, N. Bilow, R. H. Boschan, R. E. Lawrence and T. J. Aponyi, Polym. Prepr., 15, 537(1974); N. Bilow and A. L. Landis, Natl. SAMPE Tech. Conf. Ser., 8, 94(1976)]. Several reviews on polyimides or acetylene-terminated prepolymers are published and discuss other acetylene containing polyimides [P. M. Hergenrother, in (H. Mark, ed.) Encyclopedia of Polymer Science and Engineering, 2nd. ed., vol. 1, John Wiley and Sons, Inc., New York, 61(1985); P. M. Hergenrother in (H. Mark, ed.) Encyclopedia of Polymer Science and Engineering, 2nd. ed., vol. 7, John Wiley and Sons, Inc., New York, 639(1987); T. Takekoshi, in (C. G. Overberger, ed.) Advances in Polymer Science, 2(1990)]. Polyimides containing pendent ethynyl groups have been reported but one reference contains an abstract only with no experimental details or polymer properties [F. W. Harris, S. M. Padaki and S. Varaprath, Polym. Prepr., 21(1), 3(1980)]. Other disclosures on polyimides containing pendent ethynyl groups contain detailed experimental information and polymer properties [B. J. Jensen, P. M. Hergenrother and G. Nwokogu, Polym. Prepr., 33(1), 914 (1992) and B. J. Jensen, P. M. Hergenrother and G. Nwokogu, Polymer, 34(3), 630, (1993)].